Interpretive Summary: Field and laboratory studies were conducted at Stoneville, Mississippi to evaluate the effects of drift retarding adjuvants with glyphosate herbicide. Laboratory studies including spray droplet analyses with a laser droplet analyser and spray patterns were evaluated on a commercial type patternator. Field studies were conducted to evaluate control of four rweedy plant species: barnyardgrass, pitted morningglory, smooth pigweed, and nodding spurge. Spray droplet analyses indicated that glyphosate without drift retarding adjuvant produced 53% of the spray volume in droplets <144 microns, whereas, when drift retarding adjuvants were used, the percent spray volume in droplets <144 microns ranged from 31% to 47%. All but one drift retarding adjuvant provided equal or better control of the four weedy species when evaluated 2 WAT. Spray patterns were only slightly affected by the addition of drift retarding adjuvants. Overall, these studies indicated that significant reduction in drift potential can be achieved with drift retarding adjuvants, without sacrificing efficacy.

Technical Abstract:
The volume of fine, highly driftable spray droplets (<144 um diameter) of glyphosate herbicide (0.56 kg ai in 94 L of water/ha and 276 kPa pressure) was 53% for glyphosate alone and reduced by 11 to 42% with the addition of eight drift retarding compounds. At 2 weeks after treatment in the field, glyphosate-resistant soybean was not affected by any treatment; whereas, control of four weedy plant species was 65 to 85% with glyphosate alone, increased to 83 to 99% with the addition of five drift retarding compounds, not affected by two compounds and reduced to 58 to 75% with the one remaining compound. Spray patterns were not appreciably altered by the addition of the drift retarding adjuvants.